A light fixture is a device for producing, controlling, and distributing light. It is typically a complete unit consisting of one or more lamp, a socket or sockets for positioning the lamp(s) and for connecting the lamp(s) to a power supply, a covering to protect the lamp(s), optical devices for distributing the light, and mechanical components for supporting or attaching the light fixture.
“Track lighting” is a term that generally refers to a system that includes at least one such light fixture and a track or rail that is designed to support the light fixture and deliver electric power. For example, the track may be mounted at or near the ceiling surface, recessed into the ceiling, or mounted horizontally or vertically along a wall or other surface. Track lighting systems come in a variety of shapes, sizes, and configurations. Track light fixtures also come in many shapes and styles and may be designed for use with a wide variety of lamps including incandescent, halogen, metal-halide, and fluorescent. However, in the typical configuration, a track light fixture includes a housing that encloses the lamp, socket and related internal electrical and mechanical components. The housing is coupled to external mechanical components for attaching the light fixture to a track.
Optical control of track lighting system is typically accomplished by positioning the track light fixtures along the track and then aiming the positioned light fixtures at a particular target area. Often times, a light fixture will include one or more locking mechanism to lock the fixture in place once it is positioned and aimed. Other optical control techniques may rely upon reflectors, refractors, diffusers, shades, hoods, cowls, and other devices, which are either included within or mounted to the track light fixture.
“Photometric performance” is a term that broadly refers to the efficiency and effectiveness with which a luminaire delivers light to an intended target and is often described in terms of various light distribution characteristics of a luminaire. For example, a “luminous intensity distribution curve” may be used to represent the variation of luminous intensity in a plane through the light center of the luminaire. The term “beam spread” is also used to refer to the angle between two directions in a plane in which the intensity is equal to a certain percentage of the maximum beam intensity. When that intensity is 50% of the maximum intensity through the nominal beam centerline, then the term “beam angle” is also used.
Various mechanisms have been suggested for controlling beam spread and other photometric performance characteristics of track lights and other luminaires. According to “Marks' Standard Handbook for Mechanical Engineers,” eighth edition, which is also incorporated by reference herein in its entirety, such mechanisms include, but are not limited to, linkages, cams, hoists, and/or elliptical trains. A “cam” is usually a plate or cylinder which communicates motion to a follower by means of its edge or a groove cut in its surface. However, other types of cam mechanisms are also known.
U.S. Pat. No. 7,160,001 to Bartlett et al., which is incorporated herein by reference in its entirety, describes a focus mechanism for a luminaire in which a mounting cup is axially translated relative to a stationary reflector to adjust the light beam spread of the luminaire. Although the focus mechanism of that patent is highly successful, more efficiently constructed focus mechanisms are possible.
Lamps in a track light fixture must typically be replaced or maintained at regular intervals, so as to keep the light fixture in working order. In most track light fixtures, however, accessing the lamps can be relatively difficult and/or time consuming. Often, a portion of the housing, such as a lens assembly, must be removed in order to access the interior of the housing. Also, unless the light fixture is moved out of its desired position, the housing itself may often obstruct the view of the socket. Thus, once the lamp replacement or maintenance is complete, the light fixture must be repositioned to direct light to the target location. This process is inefficient, particularly where a large number of lamps must be replaced or maintained.